This invention relates generally to the harvesting of grain and is particularly directed to the separation of chaff and grain in a combine.
A combine is an agricultural vehicle used in the harvesting of crops. The combine is typically self-propelled and is comprised of a forward header assembly and an aft drive and processing section. The header assembly typically is substantially wider than the aft portion of the combine and includes a plurality of spaced corn or row crop heads which are adapted for engaging the crops and removing the grain therefrom. The thus removed grain, in combination with crop residue such as husks in the case of corn harvesting, is then automatically delivered to the aft drive and processing section of the combine. In addition to housing the source of propulsion, such as a diesel engine and operator controls, the aft portion of the combine also includes a complicated threshing system for further separating the grain from the crop residue and for offloading the thus separated grain from the combine into a transport vehicle such as a truck. The crop residue is then exhausted from an aft portion of the combine and deposited in the field being harvested.
The threshing system includes many stages for separating the grain from the husk or leafy portion of the plant. An early stage of the threshing system typically includes a rotating cylinder operating in conjunction with a concave structure positioned adjacent to and below the cylinder to initiate grain-crop residue separation. The thus separated grain is then subjected to additional processing for further separation, while the crop residue, or chaff, is exhausted from the combine.
The additional processing to which the grain is subjected typically includes a vibrating sieve arrangement upon which the grain and chaff mixture is deposited. This sievelike structure, frequently referred to as a "chaffer", allows the grain to fall under the influence of gravity, while retaining chaff in separating the grain and chaff. Because the grain and chaff are frequently deposited upon the chaffer in a thick, mat-like mass, air is directed upward through the chaffer to break up this mat-like mass and blow the chaff upward for removal. While facilitating grain and chaff separation to some extent, this prior art approach has produced undesirable effects which actually retard the threshing operation. For example, the upward air blast through the sieve-like chaffer creates turbulence within the threshing stages which not only inhibits chaff removal from the combine, but also frequently recirculates the chaff from later to earlier threshing stages. This increases the time required for grain-chaff separation, slowing down the threshing operation, and necessitates additional work by the combine resulting in increased wear and tear on the combine as well as increased fuel consumption. Increased air turbulence within the combine also inhibits settling of the grain under the influence of gravity in a lower portion of the combine and tends to maintain the grain suspended, resulting in the discharge and loss of substantial quantities of grain from the aft of the combine.